The invention is concerned with patient tables which need to be moved horizontally or vertically during treatment or investigation.
Such tables may be found, for example, in scanning equipment such as Magnetic Resonance Imaging (MRI) equipment where typically, a patient needs to be raised or lowered to a correct height and moved into the field of influence of a superconducting magnet. Existing patient tables are moved by means of electric motors mechanically coupled to the table by systems such as lead screws. Problems arise with this arrangement due to interaction between the magnetic/electric fields associated with the motor and the scanning equipment. In order to operate, the motors have to be situated in areas of low magnetic field or be heavily shielded. Also, the motors cause electrical noise which can interfere with the scanners electrical systems. This is a particular problem if the table is moved during the scanning sequence.
Other equipment such as patient cooling fans and solenoid operated switches give rise to similar problems of interaction with electric motors. Existing equipment such as MRI scanners employ cryogenic refrigeration means to maintain the temperature of the superconducting magnet at a value below which quenching occurs. (This is a process in which the magnet undergoes a transition to a normal conducting state). The valves used to control the delivery and return of cryogenic refrigerant are typically electrically operated and hence provide another source of unwanted interference with the scanning equipment.
Applicant's co-pending United Kingdom Patent Application number GB0520389.8 describes a cryogenic refrigerator comprising a rotary valve which controls the flow of high pressure gas into the refrigerator and the return of the gas from the refrigerator, wherein a rotary fluid motor is arranged to drive the rotary valve.
MRI scanners also include a gradient coil, which is effectively a tube of resin with electrical coil windings and cooling tubes embedded into it. Temperature control is assisted by pumping cooling fluid around the gradient coil. The pressure drop across the gradient coil in these systems is typically 2 Bar. Hence existing equipment designs include plumbing arrangements able to deliver fluid to the vicinity of the equipment and able to cope with such fluid pressures.
The present invention is directed, which may be, for example, a Magnetic Resonance Imaging (MRI) scanner having a gradient coil, with the fluid being directed to the vicinity of said gradient coil. The apparatus may also include means for preventing flow of fluid to the gradient coil while the hydraulic pistons or motors are operated, as well as means for directing fluid to other components of the apparatus, for example a hydraulic motor arranged to drive a patient cooling fan or cryogenic fluid delivery valves.
The invention is also directed towards a method of operating the apparatus such as an MRI scanner, the method comprising the step of cooling a gradient coil by directing the fluid thereto. The flow of fluid to the gradient coil may be prevented during the step of moving the table and fluid could be directed to other components of the MRI scanner such as a hydraulic motor arranged to drive a patient cooling fan or cryogenic fluid delivery valves.
The invention uses hydraulic pistons (cylinders) or motors to provide the motive force necessary to move a component such as a patient table. Thus, the problems of interference between the electric motors and the electrical scanning equipment are avoided. Moreover, use of a single fluid for both cooling and hydraulics reduces the additional space and reworking of existing designs necessary, which in turn provides a cost benefit.
A major advantage of the invention is that it can be produced through upgrading of existing systems. Thus an existing apparatus having a cooling system which directs coolant fluid to components of the system, and also employs motors (e.g., electric motors) for moving components, can be upgraded by replacing the motors with a hydraulic piston or motor; modifying the coolant fluid conduits so that fluid is also directed to the hydraulic piston or motor and employing a fluid suitable for acting as coolant and hydraulic fluid in the system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.